Polymeric articles because of their inherent properties are replacing glass in many end use applications, such as bottles, packaging, containers, window panes, light covers, shower doors, and the like. Some of these applications are enhanced by a "frosted" look either for practical reasons such as to block sight through the material or for aesthetic reasons. Glass is normally made frosted by etching the surface of the glass to create a light scattering and thus the frosted look is achieved. Because many polymerics cannot withstand a mechanical etching process such as sandblasting, other methods must be used to achieve the frosted appearance. To create the frosted glass look in polymeric articles, those skilled in the art will etch the mold by sandblasting or other means to give a rough surface on the mold. The rough surface on the mold transfers to the moldable polymeric article, thus creating a frosted appearance.
The practice of altering the molds is an expensive process because the mold cannot be used again for non-frosted articles. Many molding machines for polymerics have multi-cavity molds and thus several cavities must be altered. Injection blow molding is a common process used to produce bottles. The molds for this process cost from about $100,000 to $200,000, thus making the increased inventory of molds uneconomical. Also, some polymeric materials such as polyvinyl chloride (PVC), when injection blow molded into bottles, have a low pressure applied to the PVC during the molding process, such that the PVC would not be forced into the mold at sufficient pressure to transfer a small surface roughness to the PVC bottle. This explains the absence of frosted PVC bottles from the marketplace, even though they are desired by customers.
For the rare polymeric materials which can withstand a post molding treatment of etching, the post molding treatment is an added process which adds greatly to the cost of the article.
It would be desirable to have a process which could produce frosted polymeric articles which did not involve etching the mold or an abrasive aftertreatment, and which could be molded in conventional smooth molds.